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Add ALSA channel mapping support

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This commit is contained in:
Cameron Gutman 2021-08-21 20:08:58 -05:00
parent 87613b3176
commit 72985ee71d
1 changed files with 75 additions and 14 deletions
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89
src/audio/alsa.c
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@ -36,25 +36,11 @@ static int alsa_renderer_init(int audioConfiguration, POPUS_MULTISTREAM_CONFIGUR
int rc;
unsigned char alsaMapping[AUDIO_CONFIGURATION_MAX_CHANNEL_COUNT];
/* The supplied mapping array has order: FL-FR-C-LFE-RL-RR-SL-SR
* ALSA expects the order: FL-FR-RL-RR-C-LFE-SL-SR
* We need copy the mapping locally and swap the channels around.
*/
memcpy(alsaMapping, opusConfig->mapping, sizeof(alsaMapping));
if (opusConfig->channelCount >= 6) {
alsaMapping[2] = opusConfig->mapping[4];
alsaMapping[3] = opusConfig->mapping[5];
alsaMapping[4] = opusConfig->mapping[2];
alsaMapping[5] = opusConfig->mapping[3];
}
samplesPerFrame = opusConfig->samplesPerFrame;
pcmBuffer = malloc(sizeof(short) * opusConfig->channelCount * samplesPerFrame);
if (pcmBuffer == NULL)
return -1;
decoder = opus_multistream_decoder_create(opusConfig->sampleRate, opusConfig->channelCount, opusConfig->streams, opusConfig->coupledStreams, alsaMapping, &rc);
snd_pcm_hw_params_t *hw_params;
snd_pcm_sw_params_t *sw_params;
snd_pcm_uframes_t period_size = samplesPerFrame * FRAME_BUFFER;
@ -88,6 +74,81 @@ static int alsa_renderer_init(int audioConfiguration, POPUS_MULTISTREAM_CONFIGUR
CHECK_RETURN(snd_pcm_sw_params(handle, sw_params));
snd_pcm_sw_params_free(sw_params);
/* Determine the ideal mapping for a given channel count */
snd_pcm_chmap_t* chmap;
switch (opusConfig->channelCount)
{
case 2:
chmap = snd_pcm_chmap_parse_string("FL FR");
break;
case 6:
chmap = snd_pcm_chmap_parse_string("FL FR RL RR FC LFE");
break;
case 8:
chmap = snd_pcm_chmap_parse_string("FL FR RL RR FC LFE SL SR");
break;
default:
fprintf(stderr, "Unsupported channel count: %d\n", opusConfig->channelCount);
return -1;
}
/* If we have a channel map, try to apply it */
if (snd_pcm_set_chmap(handle, chmap) != 0) {
snd_pcm_chmap_t* native_chmap = snd_pcm_get_chmap(handle);
if (native_chmap != NULL) {
/* We couldn't apply our channel map, so we'll match the current map */
free(chmap);
chmap = native_chmap;
}
else {
/* We couldn't even get the native layout. We'll just hope for the best */
fprintf(stderr, "Failed to get ALSA channel map. Surround audio channels may be incorrect!\n");
}
}
char chmap_str[512];
snd_pcm_chmap_print(chmap, sizeof(chmap_str), chmap_str);
printf("ALSA channel map: %s\n", chmap_str);
/* The supplied mapping array has order: FL-FR-C-LFE-RL-RR-SL-SR
* We need copy the mapping locally and swap the channels around.
*/
memcpy(alsaMapping, opusConfig->mapping, sizeof(alsaMapping));
for (int i = 0; i < chmap->channels && i < AUDIO_CONFIGURATION_MAX_CHANNEL_COUNT; i++) {
switch (chmap->pos[i]) {
case SND_CHMAP_FL:
alsaMapping[i] = opusConfig->mapping[0];
break;
case SND_CHMAP_FR:
alsaMapping[i] = opusConfig->mapping[1];
break;
case SND_CHMAP_FC:
alsaMapping[i] = opusConfig->mapping[2];
break;
case SND_CHMAP_LFE:
alsaMapping[i] = opusConfig->mapping[3];
break;
case SND_CHMAP_RL:
alsaMapping[i] = opusConfig->mapping[4];
break;
case SND_CHMAP_RR:
alsaMapping[i] = opusConfig->mapping[5];
break;
case SND_CHMAP_SL:
alsaMapping[i] = opusConfig->mapping[opusConfig->channelCount >= 8 ? 6 : 4];
break;
case SND_CHMAP_SR:
alsaMapping[i] = opusConfig->mapping[opusConfig->channelCount >= 8 ? 7 : 5];
break;
default:
alsaMapping[i] = 0xFF; /* Silence */
break;
}
}
free(chmap);
decoder = opus_multistream_decoder_create(opusConfig->sampleRate, opusConfig->channelCount, opusConfig->streams, opusConfig->coupledStreams, alsaMapping, &rc);
CHECK_RETURN(snd_pcm_prepare(handle));
return 0;